【作者】 向新；

【导师】 易克初；

【作者基本信息】 西安电子科技大学 ， 信号与信息处理， 2009， 博士

【摘要】 UWB(即超宽带)通信技术是本世纪初开始兴起的一项新兴的通信技术,其中脉冲无线电超宽带技术(IR UWB)是其中一个重要的技术分支。该技术在密集多径环境下具有特殊的优势。但若实现最佳接收,在信道估计以及同步等方面需要付出的代价不是简单的系统结构可以承受的,因此次最佳的自相关接收技术受到人们的重视。本文主要针对自相关类型超宽带接收机开展研究,另外还针对超宽带技术所面临的一些基本问题,如信道容量、频谱特性等开展深入的探讨,取得的主要成果有：(1)现有常规超宽带通信均定位于短距离(数十米以内)高速通信应用,本文从信息论的角度讨论了远距离超宽带通信的可行性。研究表明超宽带技术在某些特殊情况下也可应用于远距离通信,只不过不像近距离通信应用的优势那样明显。论文给出了基于地空应用的远距离UWB“两簇”信道模型假设,分析了多普勒效应的影响,提出了针对UWB信道的相干时间的概念。此外,进一步对超宽带信道容量以及结合MIMO的信道容量进行了分析,得到了具有指导意义的结果。(2)超宽带系统要求与其它无线系统具有良好的共存性能,因此,其发射功率谱密度在频域的分布必须合理,以便尽可能少干扰其它无线系统,这是一个重要问题。本文针对常规的跳时超宽带信号的频谱特性进行了研究,发现常规的跳时操作对频谱的平滑作用常常显得不够充分,而残留一些功率谱密度较大的谐波频点；为了改善这种频谱特性,在分析CPPM和PCTH调制方式的基础上,提出了一种新的伪混沌脉冲位置调制(PCPPM)方式,其综合性能得到明显的改善。性能分析和仿真实验结果验证了这个结论。(3)超宽带系统中自相关接收机的性能分析是一项基础研究工作。本文在总结现有结论的基础上,对自相关接收技术进行了分类；提出了PPM调制的TR和DIFF接收机,完善了适用的调制方式；并提出了相应的GLRT最佳接收机,作为性能参考的基准。此外,论文对自相关类型接收机均进行了性能分析。(4) MIMO技术和UWB技术的结合是实现高速传输的重要途径,但复杂度较高。为了降低实现复杂度,研究发现UWB和MIMO相结合具有一些独特的优势,比如在UWB中简单的发射分集就会有性能增益,这与窄带系统是不同的；论文进一步提出了一种TR-MIMO-UWB技术方案,该方案无需信道估计,且易于实现。性能分析表明该方案是可行性。(5)本文在分析TDT盲定时算法的基础上,提出了一种适用于PPM调制的TS-TDT盲定时算法,该算法采用两条相关支路计算延迟互相关值从而获得同步信息。理论分析和仿真结果表明该算法具有较低的复杂度和在精度控制方面具有灵活性。更多还原

【Abstract】 Ultra-wideband (UWB) communication is a rising communication technology, where impulse radio based UWB (i.e., IR-UWB) is the most important branch. It has particular advantages in dense multipath channels. Optimal receiver can be used in IR-UWB system, but its complexity is often unceptable, where channel estimaton and synchronization are two chanlleging problems. Therefore, it is necessary to explore new technology with low complexity. This dissertatation focuses on autocorrelation UWB receiver. Besides, we analyze some basic problems in depth, such as channel capacity and spectrum characteristic, etc., The main contributions are as follows:(1)Different from the convention UWB system is usally aiming at high data rate communication over short distances, the dissertation discusses the feasibility of communication over long distances basing on information theory. The research results show that UWB also suits low speed communications over long distances under some special situations, while its superiority could be probably not remarkable as that in short distance communications. A "Two Cluster"supposition of long distance UWB channel model is proposed for ground-aircraft communication applications, Doppler effect and coherence time of UWB channel are proposed and analysised too. In addition, channel capacity the UWB system combined with MIMO are analyzed and some useful results are obtained.(2) Since the UWB system is required to have co-existence capability with other wireless systems, it is very important that its transmited signals must be seasonablly distributed in the frequency domain so as to interfere the latters as less as possible. After analyzing the distribution of the power spectral density of the Time-Hopping-UWB (i.e. TH-UWB) signals, the dissertation reveals that the conventional TH operation is not good enough to smooth the spectrum, which makes some residue existed in harmonic frequency points. In order to improve the properties of the spectrum, a novel pseudo chaotic pulse position modulation (PCPPM) is proposed based on analyzing CPPM and PCTH modulations, which has its comprehensive performance dramatically improved. It has been validated by means of performance analysis and simulation experimental results.(3) About the performance of the UWB autocorrelation receiver, the dissertation has classified them and analyzed their performance basing on the existing conclusion. The Transmission Reference(TR) and DIfferential (DIFF) receiver with PPM modulation are proposed, and their modulation mode is improved. The dissertation suggests that the Generalized-Likelihood-Radio-Test (GLRT) receiver of UWB could be regarded as a reference standard for the system performance. Moreover, the performance of all UWB autocorrelation receiver are analysised.(4) Combining MIMO with UWB is a very important way to realize high speed communications, but it could result in high complexity. The dissertation discover a fact, namely simply transmit diversity is effective in UWB, which is different from the convention narrow system. In addition, the dissertation proposes a noval scheme with low complexity receiver, called as TR-MIMO-UWB. The proposed scheme is easy to implement, and needn’t channel estimation. The performance analysis shows that the scheme is feasible.(5) Basing on analysis of TDT blind timing algorithm, the dissertation proposes a Time-Shift-TDT(TS-TDT) blind timing algorithm to deal with timing synchronization for PPM-UWB, which gets synchronizing information from calculating the delay cross-correlation values by means of two correlation branches. Theoretical analysis and simulation results demonstrate that the implementation of this algorithm is of low complexity and flexible in precision control.更多还原